I've read quite a few posts on imdb.com debating whether Mrs. Spool was able to do all the killings since they require her to move around quickly and have the strength to lift bodies as heavy as Toomey's. but why couldn't Norman be the killer of one of them other then Mrs. Spool? He was doing all the killings in part 3, maybe he already regained his Mother half of his identity before Lila's death? He was not completely normal at the beginning since he had a hallucination of his mother talking to him right when he got home before the phone calls started. Plus the diner manager in part 3 mentioned Spool never missed a day of work and 2 of the killings ( the boy and Lila) happened in daytime not to mention the phone calls. Norman could have easily gone completely mad halfway through the film not any saner than in part 3.

Some interesting thoughts: assume Norman killed no one in this one other than Spool and Spool never went up to Norman's house at the end of part 2, would the killings have happened in Psycho 3? I mean then there would be no "Mother" at the house for Norman to talk to telling him what to do. What if Spool, Lila, and Mary never bothered Norman in 2, then would Red, Patsy, Duane, and Maureen have lived in part 3's timeline?

Sorry if this has been discussed before but I'm really hyped for the upcoming blu ray release that I want to read some feedback on this while waiting for the commentary on the BD ( hopefully there will be one!)